How to determine head height automatically

I'm creating three documents with three different headers, containing images or large banners. Is there a way to determine the head height automatically or even better a way to change the head height automatically with reference to the content?

I know LaTeX is telling me the head height is too small and I should change it to xx pt, but I would like to not have to do it manually.

A little excerpt of the beginning of one of my documents:

\documentclass[pdftex,12pt,oneside]{report}

\usepackage[pdftex]{graphicx}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{color}

\usepackage[paper = a4paper, tmargin = 2cm, bmargin = 2cm, lmargin = 2.5cm, rmargin = 2cm]{geometry}

\usepackage{fancyhdr}
\fancypagestyle{titlepage}
{
\fancyhf{}
\renewcommand{\footrulewidth}{0pt}
}
• Could you please add a minimal example? – egreg Jun 5 '13 at 20:27
• @egreg Added a little excerpt. – Chris.V Jun 5 '13 at 20:33

I do not think, it makes much sense to use an overlarge height of the titlepage's header for the whole document. Nonetheless the question is interesting in general.

Package fancyhdr already updates \headheight or \footskip, if the header or footer is too small. The following example stores the latest values of these dimension registers at the end of the document in an auxiliary file \jobname.heights. If the file exists, it is read in the preamble, before package geometry is loaded that might use the updated values for its calculations. Therefore the .aux file cannot be used for this purpose, because it is read a little too late (in \begin{document}).

\documentclass[12pt]{report}

\usepackage{atveryend}
\makeatletter
\AtVeryEndDocument{%
\if@filesw % respect \nofiles
\begingroup
% same write register as environment filecontents uses
\chardef\reserved@c=15 %
\immediate\openout\reserved@c=\jobname.heights\relax
\immediate\write\reserved@c{%
}%
\immediate\write\reserved@c{%
\string\setlength{\string\footskip}{\the\footskip}%
}%
\immediate\closeout\reserved@c
\endgroup
\fi
}
\makeatother
\InputIfFileExists{\jobname.heights}{}{}

\usepackage[
includefoot,
a6paper,
landscape,
showframe,
]{geometry}

\usepackage{fancyhdr}

\pagestyle{fancy}
\fancyhf{}
\cfoot{\Huge \begin{tabular}{c}Footer\\\thepage\end{tabular}}
\renewcommand{\footrulewidth}{0pt}

\begin{document}
Hello World
\end{document}

First run

Package fancyhdr warns:

Package Fancyhdr Warning: \headheight is too small (12.0pt):
Make it at least 30.0pt.
We now make it that large for the rest of the document.
This may cause the page layout to be inconsistent, however.

Package Fancyhdr Warning: \footskip is too small (30.0pt):
Make it at least 50.99991pt.
We now make it that large for the rest of the document.
This may cause the page layout to be inconsistent, however.

And the contents of the page is displaced:

Second run

The previously written \jobname.heights is used:

\setlength{\footskip}{50.99991pt}

There are no warnings and the page is:

Workaround for package calc

Package fancyhdr has bugs, e.g. \global\setlength that does not work, if package calc is loaded. The following code patches the macro \@fancyvbox.

\makeatletter
\def\reserved@a#1#2{\setbox0\vbox{#2}\ifdim\ht0>#1\@fancywarning
{\string#1 is too small (\the#1): ^^J Make it at least \the\ht0.^^J
We now make it that large for the rest of the document.^^J
This may cause the page layout to be inconsistent, however\@gobble}%
\dimen0=#1\global\setlength{#1}{\ht0}\ht0=\dimen0\fi
\box0}
\ifx\reserved@a\@fancyvbox
\typeout{Patching \noexpand\@fancyvbox from package fancyhdr.}
\def\@fancyvbox#1#2{%
\setbox0\vbox{#2}%
\ifdim\ht0>#1\relax
\@fancywarning{%
\string#1 is too small (\the#1): ^^J%
Make it at least \the\ht0.^^J%
We now make it that large for the rest of the document.^^J%
This may cause the page layout to be inconsistent, however\@gobble%
}%
\dimen0=#1\relax
\global#1=\ht0\relax
\ht0=\dimen0 %
\fi
\box0 %
}
\fi
\makeatother

The code should be inserted in the preamble after package fancyhdr is loaded.

• Thanks for your fast reply. Oh fancyhdr updates it already if it's too large? Nice to know. This looks really nifty and I'll try it at home right after work. The only problem left and which I probably forgot to mention is that my headers contain data in all three sections of fancyhead. Is that a problem or does your solution always choose the right \headheight? – Chris.V Jun 6 '13 at 6:02
• @Chris.V: It does not matter, how many sections of \headheight are used. – Heiko Oberdiek Jun 6 '13 at 7:45
• Yeah no that was my mistake. :) Hadn't thought the whole thing to the end. ^^ Thanks for your answer, it exactly does what I searched for. – Chris.V Jun 6 '13 at 18:35
• unfortunately this does not work with the calc package, see my question tex.stackexchange.com/q/353243/120953. David Carlisle noted there in a comment to his answer that "it isn't really safe to use \chardef\reserved@c=15 % it could be overwritten without warning by other writing in the document. It would be better to allocate a \newwrite for this use in the preamble and use that instead of 15, or just use \@auxout and write to the aux file which would simplify things and avoid having to re-input." – jakun Feb 10 '17 at 23:07
• @jakun The use of \reserved@c is perfect safe here: (1) The meaning of \reserved@c is locally defined in a group and the previous meaning of \reserved@c gets restored after the group. (2) Also, the code in the group does not expand macros and therefore unaffected by a previously defined \reserved@c. – Heiko Oberdiek Feb 10 '17 at 23:21

Not entirely true: for accentuated letters, fancyhdr ignore the accents and sets the heights to that of the selected fontsize.

Example:

\documentclass[a4paper, 12pt, twoside]{report}
\usepackage{fancyhdr}
\pagestyle{fancy}